The present invention relates to a vehicle braking apparatus and a vehicle braking method for applying a braking force to a vehicle by summing a braking force of a hydraulic braking device and a braking force of an auxiliary braking device.
Many of motor-driven vehicles, such as electric automotive vehicles and hybrid vehicles, have a regenerative braking device in addition to a hydraulic braking device to effectively utilize the limited energy. The braking force of the hydraulic braking device is referred to as xe2x80x9chydraulic braking forcexe2x80x9d, while the braking force of the regenerative braking device is referred to as xe2x80x9cregenerative braking force.xe2x80x9d This kind of motor-driven vehicles perform a cooperative control wherein the ratio of hydraulic braking force and the regenerative braking force is adequately determined to optimize the braking force applied to the vehicle as well as the storage of regenerative electric power.
FIG. 23 shows a conventional hybrid vehicle which comprises a regeneration ECU 110 sending a drive request value to each of the following electronic control units (i.e., ECUs). A motor ECU 120 controls a motor 170 via an inverter 180 based on the drive request sent from the regeneration ECU 110. The motor 170 drives front wheels of this vehicle. A battery ECU 130 monitors a charging condition of a battery 190 equipped in this vehicle. A brake ECU 140 performs a cooperative control for the regenerative braking device and the hydraulic braking device. The brake ECU 140 sends a control signal to a cooperative control valve system 150 to control the switching of this cooperative control valve system 150. A hydro booster system 160 generates a hydraulic braking force in response to a depression force applied on a brake pedal BP by a driver.
According to this hybrid vehicle, when the brake pedal BP is depressed by the driver, the brake ECU 140 calculates a target vehicle braking force corresponding to a depression amount of the brake pedal BP. In this case, the target vehicle braking force of this hybrid vehicle is substantially equal to a target braking force of an ordinary vehicle having a hydraulic braking device only. Then, the brake ECU 140 calculates a regenerative braking force determined in accordance with the target vehicle braking force. The regenerative braking force obtained by the brake ECU 140 is transmitted to the regeneration ECU 110 as a requested regenerative braking force. The regeneration ECU 110 causes the motor ECU 120 to perform a regenerative control based on the requested regenerative braking force. Then, the regeneration ECU 110 detects an actual regenerative braking force generated by the motor 170. The regeneration ECU 110 returns the detected actual regenerative braking force to the brake ECU 140 as a producible regenerative braking force. In response to this, the brake ECU 140 obtains a hydraulic braking force which is obtained by subtracting the producible regenerative braking force from the target vehicle braking force. Then, the brake ECU 140 obtains a target W/C pressure corresponding to the hydraulic braking force. In this description, W/C stands for xe2x80x9cwheel cylinder.xe2x80x9d The brake ECU 140 controls the switching of the cooperative control valve system 150 so that a W/C pressure of each wheel is equalized to the target W/C pressure.
FIG. 24 shows a schematic arrangement of a hydraulic circuit of this hybrid vehicle. Like a general braking device, the hydro booster system 160 comprises a master cylinder (hereinafter, referred to as xe2x80x9cM/Cxe2x80x9d) 161 generating a hydraulic pressure in accordance with a piston stroke, a hydraulic pump 163 supplying a pressurized oil, an accumulator 164 storing the pressurized oil supplied from the hydraulic pump 163, and a regulator 162 adjusting the pressurized oil supplied from the accumulator 164 to the same pressure level as that of the M/C 161 in proportion to a depression force applied on the brake pedal BP. A reservoir 165 is provided to supply the oil to the hydraulic pump 163.
The hydraulic pressure of the regulator 162 is transmitted to each W/C of front right, front left, rear right and rear left wheels via the cooperative control valve system 150. The cooperative control valve system 150 comprises a linear solenoid valve SLA which increases the hydraulic pressure and a linear solenoid valve SLR which decreases the hydraulic pressure. Each of the linear solenoid valves SLA and SLR is opened or closed in response to a control signal supplied from the brake ECU 140 to adjust the pressure level of each W/C. The downstream side of the cooperative control valve system 150 is bifurcated into a front oil passage 166 supplying the oil to the front right W/C and the front left W/C of the front wheels, and a rear oil passage 167 supplying the oil to the rear right W/C and the rear left W/C of the rear wheels. The front oil passage 166 comprises a switching solenoid valve SS which is usually kept open under supply of electric power. The downstream side of the switching solenoid valve SS is bifurcated into an oil passage 168 supplying the oil to the front left W/C of the front left wheel and an oil passage 169 supplying the oil to the front right W/C of the front right wheel. Each of the bifurcated oil passages 168 and 169 has a well-known ABS solenoid valve SABS consisting of a pressure increasing valve SH and a pressure reducing valve SR. Similarly, the rear oil passage 167 has an ABS solenoid valve SABS consisting of a pressure increasing valve SH and a pressure reducing valve SR. Furthermore, the rear oil passage 167 has a PandB valve provided at the downstream side of the ABS solenoid valve SABS.
The hydraulic pressure of M/C 161 is transmitted to the PandB valve and to a stroke simulator SSI generating a pedal stroke in accordance with the depression force applied by the driver. Furthermore, M/C 161 is connected to the front left W/C via a switching solenoid valve SMC1 and to the front right W/C via a switching solenoid valve SMC2. The switching solenoid valves SMC1 and SMC2 are usually kept closed under supply of electric power. Accordingly, the front right W/C and the front left W/C receive the regulator pressure in an ordinary condition.
According to the above-described hybrid vehicle, when the depression amount of the brake pedal BP is small, the regenerative braking force may be sufficient enough to supply all of the required vehicle braking force. In such a case, no hydraulic braking force is required. Accordingly, in the cooperative control valve system 150, the pressure-increasing linear solenoid valve SLA is closed. The switching solenoid valves SMC1 and SMC2 are closed, too. However, when the depression amount of the brake pedal BP is increased, the regenerative braking force may be insufficient to supply all of the required vehicle braking force. In such a case, the hydraulic braking force is required. The linear solenoid valve SLA is opened under the condition where both of the switching solenoid valves SMC1 and SMC2 are closed. Thus, the regulator pressure is supplied to each W/C. However, requiring the hydraulic braking force in this manner may encounter with a system fail wherein the valve SLA is stuck in the closed position and cannot be opened. To solve this situation, the solenoid of each valve is turned off. In this case, the switching solenoid valves SMC1 and SMC2 are opened, and the M/C pressure is transmitted to the front right W/C and to the front left W/C. Thus, the braking force is obtained in accordance with the depression amount of the brake pedal BP.
However, according to the above-described hybrid vehicle, the cooperative control valve system 150 is provided at the downstream side of the hydro booster system 160. Thus, in the installation of the switching solenoid valves SMC1 and SMC2, it is necessary to consider the possibility that the cooperative control valve system 150 or the hydro booster system 160 may be damaged. This significantly complicates the circuit arrangement.
Furthermore, if the regenerative braking device is failed, no regenerative force will be obtained. In such a case, it is necessary to promptly supply the hydraulic braking force.
In view of the above problems, the present invention has an object to provide a vehicle braking method and a vehicle braking apparatus for realizing the cooperative control without using both the conventional cooperative control valve system and the switching solenoid valves.
The present invention has another object to provide a vehicle braking method and a vehicle braking apparatus for promptly responding to an inoperable condition of the auxiliary braking device.
To accomplish the above and other related objects, the present invention provides a first vehicle braking apparatus for applying a braking force to a vehicle by summing a braking force of a hydraulic braking device and a braking force of an auxiliary braking device.
The first vehicle braking apparatus comprising:
input value detecting means for detecting a brake pedal input value;
target vehicle braking force output means for outputting a target vehicle braking force corresponding to the brake pedal input value detected by the input value detecting means;
assigned braking force output means for outputting an assigned braking force which is obtained by subtracting a minimum braking force of the hydraulic braking device corresponding to the brake pedal input value from the target vehicle braking force generated from the target vehicle braking force output means; and
braking control means for obtaining a distributive braking force of the hydraulic braking device which is obtained by subtracting the braking force of the auxiliary braking device from the assigned braking force generated from the assigned braking force output means, and for controlling the hydraulic braking device based on a target hydraulic braking force which is a sum of the minimum braking force and the distributive braking force.
According to the first vehicle braking apparatus of the present invention, in attaining a target vehicle braking force corresponding to a brake pedal input value, an assigned braking force is obtained by subtracting a minimum braking force of the hydraulic braking device corresponding to the brake pedal input value from the target vehicle braking force. Then, a distributive braking force of the hydraulic braking device is obtained by subtracting the braking force of the auxiliary braking device from the assigned braking force. And, the hydraulic braking device is controlled based on a target hydraulic braking force which is a sum of the minimum braking force and the distributive braking force.
With this arrangement, in attaining the target vehicle braking force, the present invention always utilizes the braking force of the hydraulic braking device. In other words, the first vehicle braking apparatus of the present invention does not require to perform the valve switching operation for activating or deactivating the hydraulic braking device. Accordingly, the vehicle braking apparatus of the present invention can execute the cooperative control without using the conventional cooperative control valve system and the switching solenoid valves. Thus, the hydraulic circuit can be simplified.
In the explanation of the present invention, the xe2x80x9ctarget vehicle braking forcexe2x80x9d is equivalent to a target braking force of an ordinary vehicle which uses the hydraulic braking device only. Furthermore, the xe2x80x9cbrake pedal input valuexe2x80x9d is for example a depression force applied on the brake pedal or a stroke length of the brake pedal or a M/C pressure. The xe2x80x9cminimum braking force of the hydraulic braking devicexe2x80x9d is a braking force exceeding a minimum vehicle braking force required in accordance with law regulations. The xe2x80x9cauxiliary braking devicexe2x80x9d is for example a regenerative braking device, an exhaust braking device, or an engine braking device. Furthermore, the xe2x80x9cbraking forcexe2x80x9d is used to represent a braking force itself and also conceptually used to encompass similar physical quantities, such as deceleration, which can be identified as being equivalent to the braking force.
In obtaining the assigned braking force, the first vehicle braking apparatus of the present invention does not restrict the distributive ratio between the auxiliary braking device and the hydraulic braking device. However, it is preferably in the first vehicle braking apparatus that all of the assigned braking force is supplied from the auxiliary braking device when the braking force of the auxiliary braking device is not smaller than the assigned braking force and also preferable that the hydraulic braking force is added as a supplement for filling a lack of braking force when the braking force of the auxiliary braking device is smaller than the assigned braking force. In this case, the braking force of the auxiliary braking device is supplied as much as possible for obtaining the assigned braking force. Thus, it becomes possible to suppress the abrasion of the brake pad or the brake shoe.
Furthermore, according to the first vehicle braking apparatus of the present invention, it is preferable that the hydraulic braking device comprises a M/C and a booster provided at the upstream side of the master cylinder and equipped with a boost ratio changing mechanism. And, the braking control means adjusts the boost ratio of the booster when the braking control means controls the hydraulic braking device. In this case, it is possible to equalize the M/C pressure with the W/C pressure in an ordinary braking operation (for example, in an ABS non-operating condition of an ABS equipped vehicle). It is advantageous from the viewpoint of fail safe. The xe2x80x9cboost ratioxe2x80x9d is defined as a ratio of the booster output to the brake pedal input.
The first vehicle braking apparatus of the present invention does not restrict the mechanism for controlling the boost ratio of the booster. It is however preferable in the first vehicle braking apparatus to use the mechanism capable of changing the boost ratio by forcibly changing a pedal input of the booster or by changing a pressure of operation fluid supplied to an operation chamber of a power piston of the booster. Employing such a mechanism makes it possible to provide a simple arrangement for realizing the variable boost ratio.
According to the first vehicle braking apparatus of the present invention, it is preferable that the auxiliary braking device is a regenerative braking device. Recently, research and development of motor-driven vehicles including the electric motors and the hybrid vehicles is very active. The vehicle braking apparatus of the present invention is preferable in effectively utilizing the energy in this kind of vehicles and in easily solving the system failure. If the regenerative efficiency is considered, it is desirable that all of the assigned braking force is supplied from the regenerative braking device when the braking force of the regenerative braking device is not smaller than the assigned braking force and the hydraulic braking force is added as a supplement for filling a lack of braking force when the braking force of the regenerative braking device is smaller than the assigned braking force.
Furthermore, the present invention provides a first vehicle braking method comprising the steps of:
in attaining a target vehicle braking force corresponding to a brake pedal input value,
obtaining an assigned braking force by subtracting a minimum braking force of the hydraulic braking device corresponding to the brake pedal input value from the target vehicle braking force;
obtaining a distributive braking force of the hydraulic braking device by subtracting the braking force of the auxiliary braking device from the assigned braking force; and
controlling the hydraulic braking device based on a target hydraulic braking force which is a sum of the minimum braking force and the distributive braking force.
Application of the first vehicle braking method of the present invention is not limited to the first vehicle braking apparatus comprising the above-described various means.
Furthermore, to accomplish the above and other related objects, the present invention provides a second vehicle braking apparatus for applying a braking force to a vehicle by summing a braking force of a hydraulic braking device and a braking force of an auxiliary braking device.
The second vehicle braking apparatus comprising:
input value detecting means for detecting a brake pedal input value;
target vehicle braking force output means for outputting a target vehicle braking force corresponding to the brake pedal input value detected by the input value detecting means;
assigned braking force output means for outputting an assigned braking force which is obtained by subtracting a minimum braking force of the hydraulic braking device corresponding to the brake pedal input value from the target vehicle braking force generated from the target vehicle braking force output means; and
auxiliary brake operability judging means for judging whether or not the auxiliary brake device is operable; and
braking control means for responding to judgment result of the auxiliary brake operability judging means,
wherein when the auxiliary brake operability judging means judges that the auxiliary braking device is operable, the braking control means is for obtaining a distributive braking force of the hydraulic braking device which is obtained by subtracting the braking force of the auxiliary braking device from the assigned braking force generated from the assigned braking force output means, and for controlling the hydraulic braking device based on a target hydraulic braking force which is a sum of the minimum braking force and the distributive braking force,
and further when the auxiliary brake operability judging means judges that the auxiliary braking device is inoperable, the braking control means is for controlling the hydraulic braking device based on a target hydraulic braking force which is equal to the target vehicle braking force.
According to the second vehicle braking apparatus of the present invention, in attaining a target vehicle braking force corresponding to a brake pedal input value, when the auxiliary braking device is operable, an assigned braking force is obtained by subtracting a minimum braking force of the hydraulic braking device corresponding to the brake pedal input value from the target vehicle braking force. Then, a distributive braking force of the hydraulic braking device is obtained by subtracting the braking force of the auxiliary braking device from the assigned braking force. And, the hydraulic braking device is controlled based on a target hydraulic braking force which is a sum of the minimum braking force and the distributive braking force. On the other hand, when the auxiliary braking device is inoperable, the hydraulic braking device is controlled based on a target hydraulic braking force which is equal to the target vehicle braking force. Accordingly, the present invention always utilizes the braking force of the hydraulic braking device in attaining the target vehicle braking force. Furthermore, when the auxiliary braking device is inoperable, the hydraulic braking device is immediately controlled based on the target hydraulic braking force which is equal to the target vehicle braking force without calculating the assigned braking force or without inputting the braking force of the auxiliary braking force.
In other words, the second vehicle braking apparatus of the present invention does not require to perform the valve switching operation for activating or deactivating the hydraulic braking device. Accordingly, the second vehicle braking apparatus of the present invention can execute the cooperative control without using the conventional cooperative control valve system and the switching solenoid valves. Furthermore, when the auxiliary braking device is inoperable, the second vehicle braking apparatus of the present invention can promptly supply a required braking force by the hydraulic braking device.
In the explanation of the present invention, the xe2x80x9cinoperable condition of the auxiliary braking devicexe2x80x9d is for example a failure or damage of a regenerative braking device in a case where this regenerative braking device is employed as a the auxiliary braking device of the present invention. In this case, the xe2x80x9cinoperable condition of the auxiliary braking devicexe2x80x9d includes a fully charged condition of the battery.
In obtaining the assigned braking force, the second vehicle braking apparatus of the present invention does not restrict the distributive ratio between the auxiliary braking device and the hydraulic braking device. However, it is preferably in the second vehicle braking apparatus that all of the assigned braking force is supplied from the auxiliary braking device when the braking force of the auxiliary braking device is not smaller than the assigned braking force and also preferable that the hydraulic braking force is added as a supplement for filling a lack of braking force when the braking force of the auxiliary braking device is smaller than the assigned braking force. In this case, the braking force of the auxiliary braking device is supplied as much as possible for obtaining the assigned braking force. Thus, it becomes possible to suppress the abrasion of the brake pad or the brake shoe.
Furthermore, according to the second vehicle braking apparatus of the present invention, it is preferable that the hydraulic braking device comprises a M/C and a booster provided at the upstream side of the master cylinder and equipped with a boost ratio changing mechanism. And, the braking control means adjusts the boost ratio of the booster when the braking control means controls the hydraulic braking device. In this case, it is possible to equalize the M/C pressure with the W/C pressure in an ordinary braking operation (for example, in an ABS non-operating condition of an ABS equipped vehicle). It is advantageous from the viewpoint of fail safe. Namely, in case of failure of the braking control means, the boost ratio of the booster cannot be controlled. However, in such a failed condition, it is possible to apply the hydraulic braking force generated by the M/C pressure (i.e., the minimum braking force) to the vehicle.
The second vehicle braking apparatus of the present invention does not restrict the mechanism for controlling the boost ratio of the booster. It is however preferable to use the mechanism capable of changing the boost ratio by forcibly changing a pedal input of the booster or by changing a pressure of operation fluid supplied to an operation chamber of a power piston of the booster. Employing such a mechanism makes it possible to provide a simple arrangement for realizing the variable boost ratio.
Furthermore, instead of using the booster equipped with the boost ratio adjusting mechanism, the hydraulic braking device of the second vehicle braking apparatus of the present invention can be constituted by a check valve provided in a first oil passage connecting a M/C to a W/C for maintaining a W/C pressure at a level not lower than a M/C pressure and brake fluid supply means for supplying a pressure regulated brake fluid to the W/C. In this case, the braking control means adjusts a pressure level of the brake fluid supplied from the brake fluid supply means to the W/C when the braking control means controls the hydraulic braking device. According to this arrangement, the W/C pressure is always maintained to a level not lower than the M/C pressure by the check valve provided in the first oil passage connecting the M/C to the W/C. Accordingly, when the W/C pressure caused in response to a depression of the brake pedal is lower than the M/C pressure, the check valve operates to maintain the W/C pressure to the level not smaller than the M/C pressure. In other words, when the brake pedal is depressed, the second vehicle braking apparatus of the present invention causes the hydraulic braking device to produce a hydraulic braking force not smaller than a hydraulic braking force generated by the M/C pressure (i.e., minimum braking force). If the braking control means or the brake fluid supply means is failed, the pressure regulated brake fluid will not be supplied to W/C. However, in such a failed condition, the second vehicle braking apparatus of the present invention assures that the hydraulic braking device can supply the minimum braking force.
The adjusting mechanism for adjusting the pressure of the brake fluid supplied to the W/C is not limited to a specific one. For example, it is preferable that the brake fluid supply means comprises a pump for supplying a pressurized brake fluid to the W/C, and a control valve provided in a second oil passage connecting the M/C to the W/C. This arrangement is advantageous in that the a brake fluid supply means can be simply arranged by using the pump and the control valve. In this case, the control valve maintains the W/C pressure at a value larger than the M/C pressure by a valve opening pressure. The valve opening pressure is variable. The braking control means adjusts the valve opening pressure of the control valve to adjust the pressure level of the brake fluid supplied to the W/C.
According to the second vehicle braking apparatus of the present invention, it is preferable that the auxiliary braking device is a regenerative braking device. If the regenerative efficiency is considered, it is desirable that all of the assigned braking force is supplied from the regenerative braking device when the braking force of the regenerative braking device is not smaller than the assigned braking force and the hydraulic braking force is added as a supplement for filling a lack of braking force when the braking force of the regenerative braking device is smaller than the assigned braking force.
Furthermore, the present invention provides a second vehicle braking method for applying a braking force to a vehicle by summing a braking force of a hydraulic braking device and a braking force of an auxiliary braking device. According to the second vehicle braking method, in attaining a target vehicle braking force corresponding to a brake pedal input value, when the auxiliary braking device is operable, an assigned braking force is obtained by subtracting a minimum braking force of the hydraulic braking device corresponding to the brake pedal input value from the target vehicle braking force. Then, a distributive braking force of the hydraulic braking device is obtained by subtracting the braking force of the auxiliary braking device from the assigned braking force. And, the hydraulic braking device is controlled based on a target hydraulic braking force which is a sum of the minimum braking force and the distributive braking force. On the other hand, when the auxiliary braking device is inoperable, the hydraulic braking device is controlled based on a target hydraulic braking force which is equal to the target vehicle braking force. Application of the second vehicle braking method of the present invention is not limited to the second vehicle braking apparatus comprising the above-described means. For example, in attaining a target vehicle braking force corresponding to a brake pedal input value, it is preferable to set the target vehicle braking force corresponding the brake pedal input value beforehand, and then obtain an assigned braking force by subtracting a minimum braking force of the hydraulic braking device from the target vehicle braking force. However, when the assigned braking force is constant (e.g., 0.2 G) regardless of the brake pedal input, it is preferable to directly obtain the distributive braking force of the hydraulic braking device by using this constant value without setting the target vehicle braking force.
Furthermore, to accomplish the above and other related objects, the present invention provides a third vehicle braking apparatus comprising braking control means for performing a cooperative control for applying a braking force to a vehicle by summing a braking force of a hydraulic braking device and a braking force of an auxiliary braking device.
The hydraulic braking device of the third vehicle braking apparatus comprises:
a check valve provided in a first oil passage connecting a M/C to a W/C for maintaining a W/C pressure at a level not lower than a M/C pressure; and
brake fluid supply means for supplying a pressure regulated brake fluid to the W/C, and
the braking control means is for adjusting a pressure level of the brake fluid supplied from the brake fluid supply means to the W/C in accordance with the braking force of the auxiliary braking device.
According to the third vehicle braking apparatus of the present invention, the braking control means performs the cooperative control for applying a braking force to the vehicle by summing a braking force of the hydraulic braking device and a braking force of the auxiliary braking device. The pressure of the brake fluid supplied to the W/C is determined in accordance with the braking force of the auxiliary braking device. Thus, the braking force of the hydraulic braking device is determined in accordance with the braking force of the auxiliary braking device. The third vehicle braking apparatus of the present invention always maintains the W/C pressure to a level not lower than the M/C pressure by the check valve provided in the first oil passage connecting the M/C to the W/C. Accordingly, when the W/C pressure caused in response to a depression of the brake pedal is lower than the M/C pressure, the check valve operates to maintain the W/C pressure to the level not smaller than the M/C pressure. In other words, when the brake pedal is depressed, the third vehicle braking apparatus of the present invention causes the hydraulic braking device to produce a hydraulic braking force not smaller than a hydraulic braking force generated by the M/C pressure (i.e., minimum braking force). The maximum value of the braking force of the auxiliary braking device is obtained by subtracting the minimum braking force of the hydraulic braking device from the vehicle braking force. If the braking control means or the brake fluid supply means is failed, the pressure regulated brake fluid will not be supplied to W/C. However, in such a failed condition, the third vehicle braking apparatus of the present invention assures that the hydraulic braking device can supply the minimum braking force.
Accordingly, the third vehicle braking apparatus of the present invention does not require to perform the valve switching operation for activating or deactivating the hydraulic braking device. Thus, the third vehicle braking apparatus of the present invention can execute the cooperative control without using the conventional cooperative control valve system and the switching solenoid valves. The hydraulic circuit can be simplified. Furthermore, from the view point of fail safe, providing the check valve is advantageous compared with the conventional hydraulic circuit.
The brake fluid supply means of the third vehicle braking apparatus of the present invention is not restricted to a specific one as far as it can supply the pressurized brake fluid regulated by the braking control means to the W/C. For example, it is preferable that the brake fluid supply means comprises a pump for supplying a pressurized brake fluid to the W/C, and a control valve provided in a second oil passage connecting the M/C to the W/C. This arrangement is advantageous in that the brake fluid supply means can be simply arranged by using the pump and the control valve. In this case, the control valve maintains the W/C pressure at a value larger than the M/C pressure by a valve opening pressure. The valve opening pressure is variable. The braking control means adjusts the valve opening pressure of the control valve to adjust the pressure level of the brake fluid supplied to the W/C.
For example, as a practical arrangement, it is preferable that the third vehicle braking apparatus of the present invention comprises:
input value detecting means for detecting a brake pedal input value;
target vehicle braking force output means for outputting a target vehicle braking force corresponding to the brake pedal input value detected by the input value detecting means; and
assigned braking force output means for outputting an assigned braking force which is obtained by subtracting a minimum braking force of the hydraulic braking device corresponding to the brake pedal input value from the target vehicle braking force generated from the target vehicle braking force output means,
wherein the braking control means is for obtaining a distributive braking force of the hydraulic braking device which is obtained by subtracting the braking force of the auxiliary braking device from the assigned braking force generated from the assigned braking force output means, and for controlling the brake fluid supply means of the hydraulic braking device based on a target hydraulic braking force which is a sum of the minimum braking force and the distributive braking force.
In this case, in attaining a target vehicle braking force corresponding to a brake pedal input value, an assigned braking force is obtained by subtracting a minimum braking force of the hydraulic braking device corresponding to the brake pedal input value from the target vehicle braking force. Then, a distributive braking force of the hydraulic braking device is obtained by subtracting the braking force of the auxiliary braking device from the assigned braking force. And, the brake fluid supply means of the hydraulic braking device is controlled based on a target hydraulic braking force which is a sum of the minimum braking force and the distributive braking force. The xe2x80x9cminimum braking force of the hydraulic braking devicexe2x80x9d is a hydraulic braking force caused by the M/C pressure which is always produced for attaining the target vehicle braking force.
In obtaining the assigned braking force, the third vehicle braking apparatus of the present invention does not restrict the distributive ratio between the auxiliary braking device and the hydraulic braking device. However, it is preferably in the third vehicle braking apparatus that all of the assigned braking force is supplied from the auxiliary braking device when the braking force of the auxiliary braking device is not smaller than the assigned braking force and also preferable that the hydraulic braking force is added as a supplement for filling a lack of braking force when the braking force of the auxiliary braking device is smaller than the assigned braking force. In this case, the braking force of the auxiliary braking device is supplied as much as possible for obtaining the assigned braking force. Thus, it becomes possible to suppress the abrasion of the brake pad or the brake shoe.
The third vehicle braking apparatus of the present invention controls the W/C pressure to be not smaller than the M/C pressure. The check valve is always closed. Accordingly, when the driver depresses the brake pedal, the M/C pressure increases. However, the pedal stroke becomes very small or does not increase because the brake fluid remains continuously in the M/C. Thus, the driver may feel strange. When the assigned fluid pressure (i.e., a distributive braking force of the hydraulic braking device relative to the assigned braking force) is reduced due to the regenerative cooperation, the oil equivalent to the reduced M/C pressure returns to the M/C. Thus, the pedal is returned back correspondingly. The relationship between the vehicle deceleration and the pedal stroke is undesirably changed in accordance with a distribution ratio between the auxiliary braking force and the hydraulic braking force of the assigned braking force. Thus, the driver may feel strange. To solve these problems, according to the third vehicle braking apparatus of the present invention, it is preferable that the M/C is connected to a stroke simulator causing a pedal stroke according to the brake pedal input. This arrangement is preferable in that excellent brake feeling is obtained by the function of the stroke simulator.
According to the third vehicle braking apparatus of the present invention, it is preferable that the auxiliary braking device is a regenerative braking device. If the regenerative efficiency is considered, it is desirable that all of the assigned braking force is supplied from the regenerative braking device when the braking force of the regenerative braking device is not smaller than the assigned braking force and the hydraulic braking force is added as a supplement for filling a lack of braking force when the braking force of the regenerative braking device is smaller than the assigned braking force.